If it's in the headliner above your head, its an internal temp sensor for the auto HVACs. The onstar mic is in the console above the mirror.
The temp sensor is a thermistor with a small fan that blows air across it. It is the small fan that is noisy.

If it's in the headliner above your head, its an internal temp sensor for the auto HVACs. The onstar mic is in the console above the mirror.
The temp sensor is a thermistor with a small fan that blows air across it. It is the small fan that is noisy.

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Rayvoy is correct. It is a hvac sensor. They are easy to take out, just pull down on the grill part and it will pop off. Then slide your hand on top of the headliner and grab it. (might need to remove your visor for more room) I use a screwdriver thru the hole where the grill sat to pop off the connector. Then pull it out. I disassemble them, just pop the cover off and carefully bend the thermistor out of the way, then remove the fan or impeller, clean them up well, and apply a drop of gun oil or household oil to the pin and magnet looking thing that it rides on. reassemble and reinstall. The fix usually lasts about 2 years depending on the amount of dust that gets sucked into it. When they start making noise again just repeat the process.

Everyone here is right. It's the small fan in the temperature sensor for the climate controls that makes noise. Mine does the same thing and it drives me crazy. For me, it seems to only do it when its cool outside or when i first start the truck and the interior is not up to normal temperature yet.

Of course after I replied with the way I fix it, I get in my truck to take my son to school and mine is doing it now! :lol: I have not fixed it yet in this truck as I have only had it a few months. Guess I have another thing to add to the weekend to do list. Glad it is only a 10 minute job.